Author Topic: Any Mathmatitions On Line (lathe change wheels)  (Read 12053 times)

Offline doubleboost

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Any Mathmatitions On Line (lathe change wheels)
« on: August 30, 2015, 05:23:53 AM »
Hi
I have borrowed a 63 tooth change wheel to use as a conversion (metric to imperial)
This works very well
I want to make my own but can only get 64 teeth with my deviding head
As the 63 is half of a 127 (should be 63 1/2 )
How much difference would a 64 make
John

Offline shipto

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #1 on: August 30, 2015, 05:51:56 AM »
Could you rig something to use the cog you have borrowed to do a straight copy?
I also could use a 63 probably the same as yours since I believe you also own a Harrison so if you figure it out I would be interested. Also I would be interested to compare the tooth counts for the gears you have now.
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Offline mattinker

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #2 on: August 30, 2015, 06:22:31 AM »
Hi
I have borrowed a 63 tooth change wheel to use as a conversion (metric to imperial)
This works very well
I want to make my own but can only get 64 teeth with my deviding head
As the 63 is half of a 127 (should be 63 1/2 )
How much difference would a 64 make
John
Can't you make an adapter for the Sparey dividing head?

Regards, Matthew

Offline Will_D

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #3 on: August 30, 2015, 06:51:39 AM »
John,

What is your proposed gear train?

And what is your leadscrew pitch?
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Offline trapper

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #4 on: August 30, 2015, 07:51:00 AM »
How many holes do you have in your available dividing plates? As the difference you were asking 360degree divided by 63=5.714 Your thinking of cutting the nearest to that you can get with your available tooling 64teeth so 360 divided by 64=5.625 a difference of .089 of a degree.Which is less than 1/10th of a degree -so your pitch on your 64 teeth would be 1/10th of a degree closer than they should be ,not much,but be easier and more precise with the correct plate-take it you are going to do this on a mill.
« Last Edit: August 30, 2015, 02:27:15 PM by trapper »

Offline vtsteam

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #5 on: August 30, 2015, 08:35:41 AM »
Well if you're comparing to a 127, 63 is half a tooth off, and 64 is a half a tooth off, both in opposite directions. So the amount of error is the same, just depends on whether you want the pitch slightly long or slightly short.

I'm not a mathematician, so apologies if this is simplistic and inaccurate.
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Offline Swarfing

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #6 on: August 30, 2015, 09:07:01 AM »
John can't you just strap the change wheel to the back of the dividing head, rig up a locking pin against the teeth and grind a form cutter to suite the teeth? no maths and an exact copy?
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Offline vtsteam

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #7 on: August 30, 2015, 09:22:46 AM »
127 by the way is half of 254, which is the usual approximation of the number of mm in ten inches. That's how it converts the pitches.

63 and 64 are both as close as each other to half of 127 (63.5). I don't think there's much to choose between them, unless there's some other reason one is better.

127 would be better than either, but then you get into a pretty big gear to fit the trains of some lathes. That's why they go to approximately half that.
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Offline chipenter

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #8 on: August 30, 2015, 10:09:33 AM »
Can you not use the 63 gear to make a 63 ring for the divideng head ,
Jeff

Offline trapper

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #9 on: August 30, 2015, 10:37:19 AM »
The easiest way would to borrow the apropiate plate. Formula : 40/n -40/63 so a plate such as a 126hole plate would be ideal but any plate divisable by a number that can go into 63 would cut 63 teeth.Its approx 5/8turn of the crank

Offline John Stevenson

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #10 on: August 30, 2015, 11:33:00 AM »
John,
What size is the 63 teeth gear on the OD and bore details.
I have a box of old change wheels here from auctions and college clearouts, might just have one.
John Stevenson

Offline bertie_bassett

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #11 on: August 30, 2015, 02:41:30 PM »
as said by others, for a short thread I doubt it will make much difference.

lead screw pitch and other gear tooth numbers would be needed to calculate the resulting screw thread and thus the actual error.

alternatively, there are a few online gear train calculators about, might be easier to use one of them to work out what thread can be cut with a 64 tooth gear.  must be one around for a Harrison
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Offline tom osselton

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #12 on: August 30, 2015, 05:00:39 PM »
Does any of your buddies have a cnc mill?

Offline awemawson

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #13 on: August 30, 2015, 05:45:50 PM »
Is not the thread pitch error going to be constant when expressed as a percentage of nominal? So 0.5 tooth out of 63  is:

(0.5 / 63) x 100 =  0.79% as an error in pitch so a nominal 1.0 mm pitch would be 1.0079mm etc  :scratch:

So if you work out how long the thread that you are cutting is, you can easily see if the error is to much to tolerate.
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Offline John Hill

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #14 on: August 31, 2015, 12:25:56 AM »
John, I think you can make a 63 hole indexing plate!

Just cut a plate to size and clamp your borrowed 63 tooth gear centred over the plate then drill an index hole as close as you can in line with each tooth of the gear.  You now have a 63 hole divider plate.  It will not be terribly accurate but if your dividing head is 40:1 your errors will be divided by that.  If you are still not happy with the accuracy use your first plate to index and drill a second plate which will have errors 1/1600 compared to your first manual drilling.

John

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lordedmond

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #15 on: August 31, 2015, 02:44:08 AM »
John

There is a easy / expensive option fit a stepper motor to your dividing head get a  division master or similar then you can divide any division or any degree you like


Stuart

Offline fcheslop

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #16 on: August 31, 2015, 05:51:27 AM »
For odd number of teeth Iv used band saw blade round a ply former. Not very elegant but works for my simple needs
cheers
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Offline philf

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #17 on: August 31, 2015, 07:05:21 AM »
John,

Is your dividing head the BS0 type with a 40:1 worm and wheel?

If you have a division plate with 29 and 33 holes you could use compound indexing.

You need an extra detent plunger to engage with the 33 hole hole circle. (I made mine with a piece of stiffish spring steel and rivetted a pin in the end. The division plate is not bolted - it is free to rotate and the extra detent (in the back of the plate) stops it rotating.

To get 63 divisions you index 4 turns and 19 holes on the 29 hole circle and then 14 holes on the 33 hole circle by moving the plate. This doesn't give an exact division - the maximum error is 0.027 degrees.

The downside is that the chances of getting something wrong are high unless you're very, very careful.

A better solution would be for me to drill you 63 holes in a plate on my CNC mill. If you want one tell me what OD and ID. It would have to be in 3mm MS because, other than 16mm boiler plate, that's all I have. 63 holes would be very tight on a BS0 plate so the holes would have to be a bit smaller - meaning a smaller pin.

Cheers.

Phil.
Phil Fern
Location: Marple, Cheshire

lordedmond

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #18 on: August 31, 2015, 07:28:50 AM »
Phil

Could not John use his DRO on his mill to do a PDC with 63 holes or any factor of the same say 21

Stuart

Offline philf

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #19 on: August 31, 2015, 07:35:11 AM »
Phil

Could not John use his DRO on his mill to do a PDC with 63 holes or any factor of the same say 21

Stuart

Stuart,

I could easily generate a table of coordinates for John to do that - I'd just need to know the pcd of the holes. (It would be easier for me than making a plate. :thumbup:)

Edit - See Below

Cheers.

Phil.

Coordinates for holes on 100mm pitch circle with the plate centre at 0,0

   X           Y
1   0.000   50.000
2   4.978   49.752
3   9.907   49.009
4   14.738   47.779
5   19.422   46.074
6   23.913   43.911
7   28.166   41.312
8   32.139   38.302
9   35.793   34.912
10   39.092   31.174
11   42.001   27.127
12   44.494   22.811
13   46.544   18.267
14   48.131   13.542
15   49.240   8.682
16   49.860   3.737
17   49.984   -1.247
18   49.612   -6.217
19   48.746   -11.126
20   47.396   -15.924
21   45.575   -20.564
22   43.301   -25.000
23   40.597   -29.187
24   37.489   -33.084
25   34.009   -36.653
26   30.190   -39.857
27   26.072   -42.665
28   21.694   -45.048
29   17.101   -46.985
30   12.338   -48.454
31   7.452   -49.442
32   2.492   -49.938
33   -2.492   -49.938
34   -7.452   -49.442
35   -12.338   -48.454
36   -17.101   -46.985
37   -21.694   -45.048
38   -26.072   -42.665
39   -30.190   -39.857
40   -34.009   -36.653
41   -37.489   -33.084
42   -40.597   -29.187
43   -43.301   -25.000
44   -45.575   -20.564
45   -47.396   -15.924
46   -48.746   -11.126
47   -49.612   -6.217
48   -49.984   -1.247
49   -49.860   3.737
50   -49.240   8.682
51   -48.131   13.542
52   -46.544   18.267
53   -44.494   22.811
54   -42.001   27.127
55   -39.092   31.174
56   -35.793   34.912
57   -32.139   38.302
58   -28.166   41.312
59   -23.913   43.911
60   -19.422   46.074
61   -14.738   47.779
62   -9.907   49.009
63   -4.978   49.752
« Last Edit: August 31, 2015, 08:09:12 AM by philf »
Phil Fern
Location: Marple, Cheshire

Offline John Stevenson

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #20 on: August 31, 2015, 07:57:10 AM »
Phil

Could not John use his DRO on his mill to do a PDC with 63 holes or any factor of the same say 21

Stuart

21 won't work.
For one thing 21 is a standard hole sequence on dividing plate but the formulae is

40 / 63 which will not break down any lower.

We needs answers off John but he's having a lie in.
John Stevenson

Offline chipenter

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #21 on: August 31, 2015, 10:18:21 AM »
Iff you mount the 63 gear to the indexing side then every 40 teeth drill a hole in the new plate will give you 63 .
Jeff

lordedmond

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #22 on: August 31, 2015, 11:38:59 AM »
Thanks John
Had a brain fade , goes to show when you have a divisionmaster you forget the basics and just punch in the numbers , just like a calculator
Eg. Type all on one line into a calculator. 1 plus 1 divided by 2 you will get 1.5 not 1 as you expected

Reason they use BMDAS put brackets around the 1plus1 and you get 1 as you should

Moral do not trust them


Stuart
« Last Edit: August 31, 2015, 12:34:01 PM by Stuart »

Offline Pete.

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #23 on: August 31, 2015, 11:42:51 AM »
Iff you mount the 63 gear to the indexing side then every 40 teeth drill a hole in the new plate will give you 63 .

But if you mounted a 63 tooth to the indexing side then every 40 teeth cut a tooth in a blank you'd have a gear.

Offline doubleboost

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #24 on: August 31, 2015, 12:48:20 PM »
Thanks for all the comments
It would seem the 64 is no worse or better than a 63
As I am new to gear cutting I will have a go at cutting a 64
John

Offline doubleboost

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #25 on: August 31, 2015, 12:50:00 PM »
John,
What size is the 63 teeth gear on the OD and bore details.
I have a box of old change wheels here from auctions and college clearouts, might just have one.
Thanks for the kind offer John I will have a measure up

Offline doubleboost

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #26 on: August 31, 2015, 12:52:44 PM »
John,

Is your dividing head the BS0 type with a 40:1 worm and wheel?

If you have a division plate with 29 and 33 holes you could use compound indexing.

You need an extra detent plunger to engage with the 33 hole hole circle. (I made mine with a piece of stiffish spring steel and rivetted a pin in the end. The division plate is not bolted - it is free to rotate and the extra detent (in the back of the plate) stops it rotating.

To get 63 divisions you index 4 turns and 19 holes on the 29 hole circle and then 14 holes on the 33 hole circle by moving the plate. This doesn't give an exact division - the maximum error is 0.027 degrees.

The downside is that the chances of getting something wrong are high unless you're very, very careful.

A better solution would be for me to drill you 63 holes in a plate on my CNC mill. If you want one tell me what OD and ID. It would have to be in 3mm MS because, other than 16mm boiler plate, that's all I have. 63 holes would be very tight on a BS0 plate so the holes would have to be a bit smaller - meaning a smaller pin.

Cheers.

Phil.

Thanks for the offer that would be the ideal solution a direct plate
I will go with the 64 tooth gear and compare the results to the 63
Then decide from there
John

Offline trapper

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #27 on: August 31, 2015, 02:19:17 PM »
You can only try John if you havnt got the correct plate for your D/Head if it was me I would go slightly deeper on the depth

Offline Pete.

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #28 on: August 31, 2015, 04:22:35 PM »
That'll be 24 hole plate, index every 15 holes John.

Offline krv3000

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #29 on: August 31, 2015, 05:41:49 PM »
well I wood just mack a adapter to fit the 63 tooth onto the divider and set up a detent on the mill bed  :)

Offline John Hill

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #30 on: August 31, 2015, 11:20:30 PM »
I will be very disappointed John if you do not make a 63 hole indexing plate.  :coffee: You make the first one then make another from it and each time you do that the errors are averaged until you have the accuracy you require.

Thats what Henry Maudslay would have done! :bow:
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Offline trapper

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Re: Any Mathmatitions On Line (lathe change wheels)
« Reply #31 on: September 01, 2015, 06:31:34 AM »
Yes John as has been said 15holes on a 24plate it is 5/8turn you want if your going to put up with a 64tooth gear,or multiply 5/8 by whatever you have( 5/8x3=15holes24plate)5/8x4=20holes 32plate(5/8x8=40holes 64plate) etc-Good Luck